The overall objectives of this research are to provide a better understanding of the hydrodynamic behavior of circular and denatured DNA forms in aqueous electrolyte solution. Various forms of circular DNA's are being isolated from natural sources or produced artifically from naturally occurring DNA's. Viscosity and sedimentation measurements are being used to study the hydrodynamic behavior as a function of such experimental variables as pH, number of superhelical turns per unit molecular weight, ionic strength, and concentration of intercalating small molecules. In the course of these studies, which involved extensive work with the closed circular duplex DNA-containing bacteriophage PM2, it was found that this virus and its DNA have a number of properties in common with the oncogenic viruses SV40 and polyoma, which have been pursued. These include catenated forms and superhelix density heterogeneity in the replicating DNA and the existence of nucleoprotein "core particles" after partial degradation of the virus. A very interesting nuclease has been discovered in the system which was thought at first to be endogenous to the virus, which would be yet another property in common with the above oncogenic viruses; it has turned out, however, that the activity is a very persistent contaminant of PM2 phage preparations, and is in reality a product of the uninfected host bacterium of phage PM2. Future studies of this nuclease or system of nucleases will be supported by another grant.